How many supermassive black holes do you have to survey to learn more about them? You have to look at about 170,000. After a massive survey using NASA's Wide-field Infrared Survey Explorer (WISE), astronomers have poked a hole in a theory that has, until now, survived for decades.

The theory that the researchers have called into question is the unified theory of active, supermassive black holes. First developed in the late 1970s, this theory was created to explain why black holes, though similar in nature, can look completely different. The unified model proposes that every black hole is surrounded by a dusty, doughnut-shaped structure called a torus. Depending on how these "doughnuts" are positioned in space, the black holes take on different appearances.

Yet it seems as if this theory isn't true-especially after astronomers have examined the WISE results. The scientists have found evidence that something other than a doughnut structure may determine whether a black hole is visible or hidden. The unified model theory predicts that hidden black holes are simply blocked from view by doughnuts in an edge-on configuration.

"Our finding revealed a new feature about active black holes we never knew before, yet the details remain a mystery," said Lin Yan, one of the researchers, in a news release. "We hope our work will inspire future studies to better understand these fascinating objects."

In fact, WISE discovered that the galaxies with hidden black holes are more clumped together than those with exposed black holes. If tree, then astronomers will have to adjust the unified model theory to try to explain why some black holes appear hidden.

"The unified theory was proposed to explain the complexity of what astronomers were seeing," said Daniel Stern, one of the researchers, in a news release. "It seems that simple model may have been too simple. AS Einstein said, models should be made 'as simple as possible, but not simpler.'"

Want to learn more about WISE? You can check it out on the NASA website here.